on the main menu screen choose "settings", then look at top right corner... there will be a number, something like 3-1/63 or something. there are many posts that say which version it should be: 1, 2, 3 or 4 mean MK1, MK2, MK3 or MK4; 0 or 1 mean 0=b/w screen, 1=color screen; and 63 means the firmware... I think MK3 firmware development stopped at 63, MK4 - at 100 (shown on screen as 4-1/00). check the Nav forum for correct numbers and detailed explanation...